It is known to transmit data on electrical power lines. Such a type of data transmission is of particular use especially in traffic engineering in order to implement, e.g. train control or signalling.
In the prior art, broad-band transmission methods are used for transmitting data on electrical power lines. The favorite method is generally the OFDM (orthogonal frequency division multiplex) method which distributes the information to be transmitted over a very large number of mutually orthogonal carriers and transmits the composite signal of all modulated carriers in the form of a so-called OFDM burst. Accordingly, filters used for suppressing noise must have a band pass characteristic and the width of the band pass corresponds to at least the necessary band width of the composite OFDM signal. From EP 1 018 826 A2, in particular, multicarrier transmission on power systems by using an OFDM method is known in which the signal obtained by an inverse Fourier transform and corresponding to a single data burst is transmitted for a predetermined time duration (OFDM burst duration) to a receiver, these bursts following one another as closed, i.e. temporarily contiguous signal bursts. It is proposed to multiply each signal by a window function or to use a specific digital filter for the purpose of spectral limitation before the transmission.
Furthermore, in U.S. Pat. No. 4,845,466A, a system for digital high-speed information transmission in environments containing interference signals is described and a specific solution is described especially for alternating-current transmission lines, in which first the zero transition of the alternating voltage is determined by means of a sign detector and signal patterns for the noise pulses are generated with respect to the zero transition in order to enable the digital data to be transmitted to be gated out during the occurrence of the noise pulses. This solution is only specific for alternating-voltage power systems and cannot be used with direct-current supplies, on the one hand, and, on the other hand, it cannot be used at all with OFDM since the OFDM bursts mentioned must always have a fixed duration and cannot be interrupted—e.g. at the positions of noise pulses. It is especially in direct-current supplies that, generally due to the generation of the direct voltage by means of rectifiers, in particular, periodic interference signals, i.e. interference signals with precisely predetermined position in time, occur which will be called “interferers” in brief or generally noise pulses in the text which follows.
The periodic noise pulses are caused by the commutation of the current in the rectifier. The power converter components or valves, usually diodes or thyristors, in a rectifier conduct the direct current alternately. When the direct current changes from one valve to another valve, inductances between the valves crate a voltage peak which is associated with voltage rises of the order of magnitude of about 400 kV/s. Since the commutation times are determined by the frequency of the alternating current system, the noise pulses occur in a particular unchanging timing pattern, that is to say periodically.